All the noise about Donald Trump’s “hostile takeover” of the Republican Party misses a key point: Such takeovers only succeed when existing management has failed massively.

And that’s true of both the GOP and the conservative movement.

Trump’s a disrupter — but most of the fire aimed his way is just shooting the messenger.

Start with this: A few weeks ago, when Washington Post and New York Times reporters sought the Republican establishment’s reaction to Trump, the folks they dug up to talk to were a bunch of consultants and lobbyists.

That is, mercenaries — guys who get paid, win or lose.

They’re not (all) without principle, but they have a huge vested interest in the conventional fields and styles of combat that they’ve mastered — which earn them very, very good livings.

Really, they’re no different from the lefty lobbyists now cashing in from their access to Mayor Bill de Blasio.

And the Times-Post crowd wasn’t wrong: They’re the closest thing the GOP has to “wise men.” There are no sage party elders to go to.

I asked Ed Cox, the New York GOP chief, about this not long ago. His reply: “If you find the Republican establishment, let me know — I can’t find them anywhere.”

Cox is President Richard Nixon’s son-in-law; he’s been around Republican politics for five decades. If he says there’s no there there, there isn’t.

Beyond the mercenaries, you’ve got a variety of pundits and talk-radio jocks — folks whose job is to entertain a (large) niche audience. They’re focused on their niches — and inevitably view the general interest of the GOP, as well as the nation, through those blinders.

Much of the punditry’s now pointing Trump-blame fingers at the GOP “donor class” for leading the party astray — bribing pols to embrace open borders, avoid social issues, etc., etc.

It’s a fair point: You know all you need to about the donors’ political judgment by noting that they dumped $150 million on Jeb Bush — when Jeb would’ve been a low-energy loser by now even if Trump were still off doing “The Apprentice.” (The donors’ other early fave, Scott Walker, dropped out even earlier, also for cause.)

But the money men stumbled into this leading role because, ever since the Reagan years, the GOP regulars and the conservatives have been aiming for the Gipper’s second coming merely by imposing ever-stricter ideological tests.

That has produced a stream of candidates competing over who can best mouth the catechism, plus somehow pick up enough other votes to take the White House.

Today, the main alternatives to Trump are Ted Cruz and Marco Rubio — each a specialist in pushing one or another set of right-wing buttons.

Which leaves them stiff.

Cruz’s best real moment so far came when he talked about trying to get his sister out of that crack house — everything else is a rehearsed performance.

Until last week, Rubio was just a smoother, more “uplifting” Cruz. Marco’s far more loose, authentic and appealing now that he’s trading low blows with Trump — he’s a real person, rather than some bizarre savant finding the right mini-speech in his memory. Maybe the change has come in time . . .

Anyway, both offer pretty much the same “Unify the party and add a few more voters somewhere” strategy for the general election that’s been failing for the GOP since 1998.

The one time it (barely) worked, we got Dubya.

The big early achievements of the Bush presidency were, at best, technocratic, not conservative: No Child Left Behind, the new Medicare prescription drug entitlement and some temporary tax cuts.

Then came 9/11 — and soon the best and the brightest of the Republican Party gave us the Iraq debacle (much as the Democrats’ best and brightest had given us Vietnam a generation before).

After that, conventional GOP thinking gave us the John McCain and Mitt Romney nominations — neither a winner, nor even that good a competitor.

And Romney actually tried to win by reaching out to the very same voters whom Trump’s now locked up, and by using the same issues: In 2012, Mitt was a hawk on immigration and on China trade — he just couldn’t make the voters believe it.

I can’t say whether Trump will get my vote when the primaries come to our neck of the woods, but I don’t resent his existence or his success, nor blame him for destroying the GOP.